The present invention relates to a novel process for producing a curable resin having excellent heat resistance, molding property, chemical resistance, adhering property, moisture resistance and the like.
U.S. Pat. No. 4,110,364 dated Aug. 29, 1978 by Gaku et al discloses that curable resin compositions comprising a cyanate ester compound and a polyfunctional maleimide compound have excellent heat resistance, chemical resistance, adhering property, moisture resistance and the like. However, the curable resin composition containing large amount of polyfunctional maleimide component does not become uniform, because the solubility of the maleimide component in an organic solvent is poor. So workability of the curable resin composition containing a large amount of maleimide component is poor.
When a polyfunctional amine is added to the curable resin composition comprising a polyfunctional cyanate ester and a polyfunctional maleimide as a hardening agent, the resulting composition has poor storage stability, because the amine easily reacts with the cyanate ester or the maleimide. When a preliminary reaction of the curable resin composition comprising a polyfunctional cyanate ester, a polyfunctional maleimide and a polyfunctional amide is caused, the amine rapidly reacts with the maleimide and imine carbonate ester linkage is formed by reacting the amine with the cyanate ester. So the resulting cured product has poor heat resistance and the curable composition has poor storage stability.
Though a curable resin composition comprising a polyfunctional cyanate ester, a polyfunctional maleimide and trialkenyl isocyanurate (diluent) has excellent heat resistance, chemical resistance, adhering property, moisture resistance and the like, solubility of the composition in an organic solvent is poor. So the curable composition with high level of cyanate ester component or maleimide component can not be used.
In a process for producing a curable resin composition which comprises reaction a polyfunctional maleimide with a polyfunctional amine and incorporating epoxy resin into the resulting reaction product, the reaction needs a solvent, because of rapid reaction of the maleimide and the amine. So, according to the process, curable resin composition free from a solvent can not be obtained.